Structural composites are known to be useful for many applications such as electrical, aerospace, transportation and outdoor sports equipment's applications.
Isocyanate polyaddition reaction products such as polyisocyanurate comprising materials are commonly used as the polymer matrix in structural composites. The cured polyisocyanurate comprising materials are known for their good thermal, mechanical, and chemical properties but they have insufficient toughness and tend to be brittle upon cure.
In addition, the polyisocyanurate comprising materials are known to be very difficult to toughen and some may be too brittle to toughen effectively. Attempts to increase the fracture toughness in the past often came at the expense of changes (typically reduction) in modulus and of reductions in thermal properties e.g. glass transition temperature (Tg) thereby creating unacceptable limits on the applicability of the resulting composite.
For example, to increase the toughness of polyisocyanurate comprising materials, plasticizers have been added as additives giving these materials improved flexibility and durability. Most commonly phthalate esters were used as plasticizers. Plasticizers work by embedding themselves between the chains of polymers, spacing them apart (increasing the “free volume”), however, this improvement in toughness usually lead to a significant drop in modulus and glass transition temperature (Tg).
Controlling the fracture toughness of polyisocyanurate comprising materials may also be done by varying the amount of polyols having a high molecular weight. This however also leads to materials having lower glass transition temperatures and lower modulus.
Accordingly, there is a need in the industry to develop a curable polyisocyanate composition for making structural polyisocyanurate comprising composites with improved ductility (i.e. fracture toughness) while still maintaining other key processing (e.g. viscosity) and performance (e.g. glass transition temperature and modulus) properties.